Magnetic materials



2,393,295 mansrrc ms Robert P. Cross, Jr., and Joy F. Dillinger, Riverside, and Arthur N. Ogden, Chicago, 111., ore to Western Electric Gompany, Incorpo rated, New York, N. Y., a corporati York n of New No Drawing. Application October 9, 1942, Serial No. 461,448

:2 Claims. (Cl. 1os 2a7) This invention relates to magnetic materials and to a method of preparing the same, and more particularly to a magnetic material having a stabilized permeability over a given temperature range, and to a method of preparing the same.

Magnetic bodies comprising compressed, finely divided magnetic material in the form of dust or assembled thin laminations of magnetic material are extensively used as cores for loading'coils, filter coils, transformers, and similar transmission apparatus in telephone circuits. The transmission characteristics 01' such apparatus are subject to variations due to changes in permeability of the cores with temperature under service conditions. These variations are especially objectionable in the case of high quality, precislon circuits.

Objects of this invention are to provide a magnetic material having a stabilized permeability over a given temperature range and a method of.

preparing the same.

In accordance with the present invention an alloy of molybdenum, nickel and iron is obtained by powdering these materials, compacting the powdered mass and then sintering in a reducing atmosphere at a temperature below the melting point of any of the constituents. The sintered mass is then powdered and added to the material it is desired to stabilize.

Other objects and advantages of the present invention will be more apparent from the following detailed description.

As described in U. S. Patent 2,158,132, issued to V. E. Legg, May 16, 1939, a magnetic core havinga substantially constant permeability over a desired temperature range may be prepared by forming the core from amixture of dust of a normal magnetic material, such as Permalloy,

which may comprise approximately 82% nickel,

16% iron, and 2% molybdenum, and which has a positive permeability temperature coefllcient over a range of temperature from 55 F. to 95 F., and a proper amount of dust of a magnetic material having a negative permeability temperature coeflicient over that temperature range. A magnetic material having such a negative permeability coefllcient may comprise approximate- 1y 80% nickel, 12% to 13% molybdenum and the rest iron. Such a material, when used for the purpose set forth, acts as a stabilizer of the permeability of the material. However, some difliculty has been experienced in obtaining an accurately proportioned alloy due to loss of some of the molybdenum during melting these ingredients together to form an alloy.

Because a relatively high temperature is required to melt molybdenum, iron and nickel together to form an alloy, and because the melting is usually carried out in an oxidizing atmosphere, some of the molybdenum, which becomes extremely active at increased temperatures, oxidizes, and the oxide so formed volatilizes. Formation and volatilization of this oxide results in a loss of molybdenum. The loss is not constant and, since a variation of 1% in the amount of molybdenum present will cause a corresponding variation of approximately 100 F. in the Curie point of the stabilizer, it will be apparent that even a very slight loss might seriously afiect the qualities of the final product.

According to the present invention, the aforementioned metals may be efl'ectiveiy alloyed at temperatures substantially below the melting point of any of them, and without any substantial loss, by powdering the metals, thoroughly mixing the powders together, and then compacting and heating the mixture to a temperature sumcient to sinter. Since oxidation is kept at a minimum, the proportions of each are maintained substantlally constant.

In. practicing this invention, a stabilizer is prepared by powdering the desired quantities of molybdenum, nickel and iron and then mixing them intimately in a ball mill. A mixture comprising approximately nickel, 12% to 13% molybdenum and the rest iron has been formed to have a negative permeability temperature coeiilcient over a range of temperature from 55 F. to F. Adequate mixing is ordinarily obtained in approximately 30 minutes. However, it will be apparent that this time will vary with the type of mill and the quantity of material, and is not critical. The mixture is compressed and compacted into a pellet at from 100,000 to 200,000 pounds per square inch pressure and the pellet is then heated at from 1900 F. to 2000 F. for from live to six hours in a reducing atmosphere, such as hydrogen, to cause the particles to sinter.

The sintered pellet is then ground to a fine powder and the powder may then be mixed with 1 the Permalloy dust, the particles of which have stabilizing powder which will accomplish the desired stabilization being used because of the high hysteresis loss of the stabilizer material.

While this invention has been described in connection with the manufacture or a stabilized magnetic material, it will be understood that the method of this invention may be applied in many other instances, particularly where it is desired to maintain exact proportions of certain materials as described, and that while but one embodiment of this invention has been described, many changes and modifications may be made therein without departing from the spirit or scope of the present invention.

' What is claimed is:

1. A method or preparing magnetic materials comprising compacting a powdered mixture composed of 12% to 13% molybdenum, 80% nickel and the rest iron, heating the compacted mixture in a reducing atmosphere to sinter, powdering the sintered material, adding the powdered material to insulated Permalloy dust, and compacting the mixture so produced.

2. A method of preparing magnetic materials comprising compacting a powdered mixture composed of 12% to 13% molybdenum, 80% nickel and the rest iron, heating the compacted mixture in a reducing atmosphere to sinter, powdering the sintered material, adding .2% to 1% of the powdered material to insulated Permalloy dust, and compacting the mixture so produced.

ROBERT P. CROSS, JR. JOY F. DILLINGER. ARTHUR N. OGDEN. 

